It has previously been suggested to replace a grinding wheel of a grinder with a rotatable wheel having a diamond or cubic boron nitride (CBN) coated abrasive strip or belt removably mounted thereon To enable the abrasive strip to be capable of generating precision surfaces and fine finishes on a workpiece, the abrasive strip must be held on the wheel so that it always firmly engages the circumferential surface of the wheel during rotation of the wheel irrespective of the speed of rotation o the wheel.
One previously suggested means of holding a coated abrasive laminate material (CALM) strip of diamond or CBN on the wheel has been to form a rim on the wheel with a large recess or cavity inside of the rim. The wheel has only a hub, which mounts the wheel on the drive shaft of the grinder, within the recess. The rim has a transverse slot providing communication from the recess to exterior of the circumferential surface of the wheel so that the two ends of the CALM strip can enter into the recess. One end of the CALM strip is fastened by an eccentric lock, which tightens through centrifugal force during rotation of the wheel. The other end of the CALM strip is brought towards the center of the wheel and wrapped around a roller so that the end of the strip is pointed outwardly from the axis of rotation This end of the strip is attached to a metal having a specific mass and positioned close to the roller to provide for the maximum distance for any stretching of the CALM strip Rotation of the wheel causes this floating mass, through centrifugal force, to provide tension on one end of the CALM strip to keep it in its proper position. A counterbalance weight is employed to offset and correct the imbalance created by the floating mass, the roller, and the eccentric lock.
Thus, this previously suggested arrangement for retaining the CALM strip only applies a tension to one end of the CALM strip. There is no recognition of maintaining a tension on each end of the CALM strip.
Because the floating mass attached to one end of the CALM strip is free to move around after the wheel stops rotating, this mass may end up in a position in which the CALM strip is no longer wrapped around the roller. This would depend upon the position of the floating mass when the wheel stops rotating. As a result, the floating mass probably would not return to the desired position when the wheel again begins to rotate. Additionally, this unrestrained movement of the floating mass during rotation creates undesired noise.
The retention of a removable abrasive strip or belt of a rotatable wheel for a sanding machine has previously been suggested in each of U.S Pat. Nos. 1,800,805 to Pinkney and 891,857 to Perry. The retaining mechanism for the removable strip or belt of each of the aforesaid Pinkney and Perry patents includes a plurality of springs and is relatively complex and costly. The complex and costly mechanism also creates balance problems as the speed of rotation of the wheel increases. The aforesaid Pinkney patent has both ends of the belt attached to a single set of jaws that produces a tension primarily on one end of the belt as the jaws move in response to rotation of the wheel. The aforesaid Perry patent has each end of the belt attached to a separate set of jaws but only one set of jaws moves in response to rotation of the wheel to produce a tension on the end of the belt attached thereto
Each of U.S. Pat. Nos. 967,592 to Wattles and 879,504 to Wattles has a grinding or polishing wheel with a strip of a flexible abrasive material detachably secured thereto and having an adjustable tension applied to one end. The other end of the strip of each of the aforesaid Wattles patents has a beaded end for retaining it in position. This beaded end clamping arrangement is not deemed to be capable of holding the end of a strip when the wheel is subjected to a relatively high speed because the abrasive strip tends to want to move away from the circumferential surface of the wheel due to the increased centrifugal force created thereon. Furthermore, the other end of the strip of each of the aforesaid Wattles patents has a bead for retaining it in the tension applying means. It is questioned that this beaded end will remain in position to enable any stretching of the belt to be taken up by the tension supplying means.
U.S. Pat. No. 2,046,122 to Hunt discloses a buffing and polishing wheel having a cushion on its circumferential surface and on which an abrasive strip is mounted for polishing a workpiece. This arrangement cannot be used for grinding since a substantially rigid backing surface is required for the abrasive strip to bear against when grinding. This substantially rigid backing surface is not required in buffing or polishing because there is no removal of metal from a workpiece in buffing or polishing but only an improvement of the surface finish or texture of the workpiece. The aforesaid Hunt patent also has one end fixed so that tension can be applied only to one end of the strip.
When the one end of the belt is fixed a in each of the aforesaid Wattles patents, the aforesaid Perry patent, and the aforesaid Hunt patent, there is a frictional resistance when the belt is pulled on the circumferential surface of the rotatable wheel. As the wheel rotates, the tension force becomes greater while the force on the fixed end does not increase. This creates a diminishing tension near the fixed end so that the belt may move radially outwardly from the circumferential surface of the wheel due to centrifugal force, particularly as the speed of rotation of the wheel increases.
As the belt is used, it tends to stretch Since this slack can occur anywhere along the entire length of the belt, the application of a single tension force at one end of the belt may not remove all of the slack from the belt during use. If this occurs, satisfactory grinding will not occur.
In U.S. Pat. No. 3,203,079 to Monaghan, a flexible sheet has its leading or trailing edge or both clamped on a rotatable drum by a clamping strip mounted on the exterior of the rotatable drum; this cannot be used for cutting metal from a workpiece because of the presence of the clamping strip. The clamping in Monaghan of the edge or edges of the sheet occurs on the exterior of the rotating drum.
U.S. Pat. No. 4,250,810 to Fowler et al utilizes a centrifugal clamp for holding a sheet of paper wrapped around a rotating drum. The clamp either extends exterior of the drum or the drum has a very large slot Neither configuration can be employed for retaining an abrasive strip on a wheel for grinding since the transverse slot in the wheel must be as small as possible to reduce the amount of marking on the workpiece created by the absence of the abrasive strip at the slot.
The presently available CALM strips are only flexible in one direction. That is, the strip can only bend with its abrasive surface as its outer surface in the manner necessary for the CALM strip to be mounted on the circumferential surface of the rotating wheel. However, the presently available CALM strips cannot be bent in the opposite direction whereby the abrasive surface would be the inner surface of the strip. Accordingly, with the presently available CALM strips, they must not be passed around a curved surface so that they are bent in a direction whereby the abrasive surface of the CALM strip becomes the inner surface If this occurs, the CALM strip will break